JPS61251314A - Electronic tuning type receiver - Google Patents

Abstract

PURPOSE:To decrease remarkably a tracking error of a high frequency amplifier circuit by adding the 2nd tuning control voltage generating circuit having a prescribed function in addition to the 1st tuning control voltage. CONSTITUTION:The tuning control voltage generating circuit 25 is added in addition to the tuning control voltage generating circuit 11. The tuning control voltage generating circuit 25 corrects the frequency characteristic of the tuning control voltage from the circuit 11 so that the tuning frequency of tuning circuits 2, 4 follows nearly the channel selection frequency and the corrected tuning control voltage is fed to the tuning circuits 2, 4. Thus, the tuning control voltage from the tuning voltage generating circuit 11 is corrected by the circuit 25 and the result is fed to the tuning circuits 2, 4 in the high frequency amplifier circuit RA, then the tracking error of the high frequency amplifier circuit RA is reduced remarkably.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to electronically tuned receivers.

[Summary of the invention]

The present invention relates to an electronically tuned receiver, and relates to a frequency characteristic of a tuning control voltage from a first tuning control voltage generation circuit that controls the oscillation frequency of a local oscillator so that the tuning frequency of the tuning circuit approximately follows the tuning frequency. By providing a second tuning control voltage generation circuit that corrects the tuning control voltage and supplies the corrected tuning control voltage to the tuning circuit, it is possible to significantly reduce the tracking error of the high frequency amplifier circuit.

[Conventional technology]

A conventional electronically tuned FM radio receiver will be described below with reference to FIG. A signal received from the antenna (1) is supplied to a high frequency amplifier circuit RA. This high frequency amplifier circuit RA is composed of a high frequency amplifier (3) and high frequency tuning circuits (2) and (4) before and after the high frequency amplifier (3). The high frequency tuning circuits (2) and (4) each constitute, for example, a double tuning circuit, and each includes a pair of electromagnetically coupled coils LL,
L2, capacitors C and a pair of voltage-controlled variable capacitors connected in parallel with each other! Element (varactor diode) V
It consists of a series circuit of C. High frequency amplifier circuit R
The high frequency signal from A is supplied to a mixing circuit (6) that constitutes a frequency conversion circuit (5). The intermediate frequency signal obtained from the mixing circuit (6) is supplied to the frequency detection circuit (9) via the intermediate frequency amplifier circuit (8). (10) is an output terminal from which a frequency detection output is obtained. (7) is a local oscillator that constitutes the frequency conversion circuit (5), and is composed of a coil L, a series circuit of a capacitor C and a pair of voltage-controlled variable capacitance elements (varactor diodes) VC, each connected in parallel to the coil L. It is equipped with a resonant circuit (7A).

(11) is a PLL as a tuning control voltage generation circuit, and has a reference oscillator (12), a phase comparator (13), a programmable frequency divider 1B (14), and a low-pass filter (15). Then, the oscillation signal from the local oscillator (7) is supplied to the programmable frequency divider (14) and frequency-divided by 1/H, and the phase of this frequency-divided signal and the reference signal from the reference oscillator (12) is The signals are supplied to a comparator (13) for phase comparison, and the comparison output is supplied to a low-pass filter (15).

Then, the tuning control voltage obtained from this low-pass filter (15) is supplied to the cathode of each voltage-controlled variable capacitance element VC of the resonant circuit (7^) of the local oscillator (7).

Further, this tuning control voltage is also supplied to each cathode of each voltage-controlled variable capacitance element VC of each high-frequency tuning circuit (2), (4) of the high-frequency amplifier circuit RA.

In such an electronically tuned FM radio receiver, PLL (
The selected frequency is determined by selecting the frequency division ratio of the programmable frequency divider (14) of 11). That is, by changing the division ratio of the programmable frequency divider (14), the oscillation frequency of the local oscillator (7) is changed, and the oscillation frequency of the high frequency amplifier circuit RAO high frequency tuning circuit (2), (4) is changed.
The center frequency of the passband is changed to approximately match the tuning frequency.

[Problem that the invention seeks to solve]

In such conventional electronically tuned FM radio receivers, the PLL
The tuning control voltage from (11) is supplied to the voltage-controlled variable capacitance element VC of the resonant circuit (7^) of the local oscillator (7), and each high-frequency tuning circuit (2) of the high-frequency amplifier circuit RA
, (4) is also directly supplied to the variable capacitance element VC.

For this reason, a tracking error occurs in the high frequency tuning circuits (2) and (4), as shown by the broken line in Fig. 142. ! 2p, the passband center frequency (tuning frequency) of the high frequency tuning circuits (2) and (4) is set to the receiving band (for example, 7
6 MHz to 90 Ml1z), it is impossible to match the high frequency reception frequency when no modulation is performed, and in the case of FIG. 2, both sides of the reception band (the frequency is fa).

fe) so that the image frequencies match,
The frequency difference (tracking error) between the two becomes larger toward the middle. Its maximum frequency is, for example, 100k
It is about k.

The cause of this is that the tuning frequencies (resonant frequencies) of tuned circuits (resonant circuits) with different tuning frequencies (resonant frequencies) are controlled by supplying the same tuning control voltage to each voltage-controlled variable capacitance element. This is due to

If there is a tracking error in the high-frequency tuning circuits (2) and (4), the high-frequency received signal in an electronically tuned FM receiver is subject to distortion due to phase changes, and the high-frequency received signal in an electronically tuned AM receiver is attenuated. This results in decreased sensitivity.

In view of this, the present invention proposes an electronically tuned receiver that can significantly reduce tracking errors in high frequency amplifier circuits.

[Means to solve problems and relax]

The present invention provides a high frequency amplification circuit RA including tuning circuits (2) and (4), a frequency conversion circuit (5), and an intermediate frequency amplification circuit (
8), an electronically tuned receiver having a first tuning control voltage generation circuit (11) for controlling the oscillation frequency of a local oscillator (7) of a detection circuit (9) and a frequency conversion circuit (5); The frequency characteristics of the tuning control voltage from the tuning control voltage generation circuit (11) are corrected so that the tuning frequencies of the tuning circuits (2) and (4) substantially follow the tuning frequency, and this corrected tuning control Voltage tuning circuit (2), (4)
The present invention is characterized in that a second tuning control voltage generating circuit (25) is provided.

[Effect]

According to the present invention described above, the tuning voltage generation circuit (1
The tuning control voltage from 1) is transmitted to the second tuning voltage generation circuit (
25) and supplying the corrected signal to the tuning circuits (2) and (4) of the high frequency amplifier circuit RA, the tracking error of the high frequency amplifier circuit is reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Figure 1 shows an electronically tuned FM radio receiver, in which the high frequency received signal from the antenna (1) is transmitted through the high frequency amplifier circuit R.
A is supplied. This high frequency amplification circuit RA is composed of a high frequency amplifier (3) and high frequency tuning circuits (2) and (4) provided at the front and rear stages thereof. High frequency tuning circuit (2).

(4) is a series circuit consisting of, for example, a double-tuned circuit, and includes electromagnetically coupled coils LL and L2, a capacitor C and a pair of voltage-controlled variable capacitance elements (varactor diodes) VC connected in parallel to each of the coils LL and L2. It is composed of. The output of the high frequency amplifier circuit RA is the frequency conversion circuit (5)
The intermediate frequency signal obtained from this is supplied to the frequency detection circuit (9) via the intermediate frequency amplifier circuit (8), and the detected output is output to the output terminal (10). can get. (7) is a local oscillator that constitutes the frequency conversion circuit (5), and is composed of a coil L, a series circuit of a capacitor C and a pair of voltage-controlled variable capacitance elements (varactor diodes) VC connected in parallel to the coil L. It is equipped with a resonant circuit (7A) consisting of:

(11) is a PLL as the first tuning control voltage generation circuit
A reference oscillator (12), a phase comparator (13),
A local oscillation signal from a zero local oscillator (7) having a programmable fraction JiJ unit (14) and an o-lotus filter (15) is supplied to a frequency divider (14) and divided by 1/N, This frequency-divided output and the reference oscillation signal from the reference oscillator (12) are supplied to a phase comparator (13) for phase comparison, and the comparison output is supplied to a low-pass filter (15). The tuning control voltage obtained from this low-pass filter (15) is supplied to the cathode of each voltage-controlled variable capacitance element VC of the resonant circuit (7^) of the local oscillator (7).

(25) is an open control voltage generating circuit, which will be explained below. The first tuning control voltage from the PLL (11) is applied to the resistor (
18) and (19) are applied to both ends of the series circuit. The voltage obtained from the midpoint of the connection between the resistors (18) and (19) is supplied to the non-inverting input terminal of the operational amplifier (16). A resistor (20) is connected between the output terminal and the inverting input terminal of the operational amplifier (16).

The detection output of the frequency detection circuit (9), ie, the audio signal, is supplied to the non-inverting input terminal of the operational amplifier (21).

A resistor (22) is connected between the output terminal and the inverting input terminal of the operational amplifier (21). Then, the operational amplifier (2
The output terminal of 1) is connected to the operational amplifier (
16) is connected to the inverting input terminal. Buffer amplifier (
The output of 17) is supplied to a window comparator (24) and compared with, for example, five reference voltages, and depending on which region among the five reference voltages it falls within, the output of 41
Generates a comparison output of ft'JI. Operational amplifier (21)
The inverting input terminals of the on/off Z switches 81 to S4,
It is grounded through series circuits of resistors R1 to R4 and DC power supplies E1 to E4, respectively.

The tuning control voltage from the operational amplifier (16) is applied to each high frequency tuning circuit (2) of the high frequency amplifier circuit RA.

(4) is supplied to the cathode of each voltage-controlled variable capacitance element YC.

Next, the operation of this electronically tuned FM radio receiver will be explained. Tuning can be performed by varying the frequency division ratio of the programmable frequency divider (14) of the PLL (11). That is, by changing the frequency division ratio of the programmable frequency divider (14), the local oscillation frequency of the local oscillator (7) changes, and each high frequency tuning circuit (2) of the high frequency amplifier circuit RA changes.

Tracking is performed so that the bandpass center frequency in (4) substantially coincides with the tuning frequency, that is, the carrier frequency of the high-frequency received signal.

By the way, the relationship between the capacitance and control voltage of a voltage-controlled variable capacitance element (varactor diode) is non-linear, and in the case of a tuned circuit using this, as the tuning frequency increases, the control voltage to obtain the same frequency deviation increases. The deviation will be large. That is, the control voltage is proportional to the second to third power of the tuning frequency. Therefore, taking this point into consideration, the gain of the operational amplifier (21) is
Change it by polygonal line approximation as follows. That is, the tuning control voltage from the buffer amplifier (17) is supplied to the window comparator (20), and the reference voltages Va, vb, Vc, Vdl Ve (however, Va < V
Compare b<Vc<Vd<Ve). Then, depending on which of the four regions between the reference voltages Va to Ve the tuning control voltage is in, the switches 81 to S4 are selectively turned on to change the gain of the operational amplifier (21) to the resistor R.
By changing the resistance values of 1 to R4, the detection output voltage of the detection circuit +1 (9) is corrected, and the relationship between the tuning frequency and control voltage of the open circuits (2) and (4) is as follows: Try to match the above characteristics.

Furthermore, the reception frequency band (e.g. 76MHz to 90MI (
z) In the high frequency tuning port v! I(2), (
4) The tuning control voltage from the buffer amplifier (17) is controlled by the DC power supplies E1 to E4 according to the voltage so that the passband center frequency (tuning frequency) approximately matches the tuning frequency (high frequency reception carrier frequency). and the operational amplifier (2
1) Correct by changing the offset voltage.

Note that the frequency detection output voltage supplied to the non-inverting input terminal of the operational amplifier (21) is V4, the output voltage of the operational amplifier (21) is V3, and the output voltage of the buffer amplifier (17) is V1.
% The output voltage of the operational amplifier (16) is assumed to be v2. Then, when V3=0, the gain of the operational amplifier (16) is controlled so that V2=1.

Figure 2 shows the frequency characteristics of the tracking error when the tuning control voltage from the PLL (11) is directly supplied to each voltage-controlled variable capacitance element VC of each high-frequency tuning circuit (2) and (4). As shown by the broken line, for example, if it has a downwardly convex characteristic, each tuning circuit (2),
The control voltage supplied to each voltage-controlled variable capacitance element VC in (4) need only have the opposite characteristics. Therefore, the high frequency reception frequency range is set between frequencies fa and fe, and the range is divided into four equal parts, and the reference frequency f including both ends is set as
a, f5. fc, fat r, and approximately average control voltages Vα, Vβ, Vγ in each region.

Va is obtained from the above-mentioned DC power supplies Es to E4. That is, the voltage having the frequency characteristic shown by the solid line in Fig. 2 is applied to the operational amplifier (
The voltage on the output side of 21) is 3.

In addition, the gain of the operational amplifier (21) is made different in each region between the above-mentioned frequencies by the resistors Rs to R4, and is supplied to each voltage-controlled variable capacitance element VC of the tuning circuits (2) and (4). By varying the slope of the control voltage, the tuning control voltage with frequency characteristics as shown in Figure 3 is obtained.
2 is obtained at the output terminal of the operational amplifier (16), and is supplied to each cathode of each voltage-controlled variable capacitance element VC of each tuning circuit (2) and (4>).

In addition, each switch is omitted, one variable resistance element such as FET is used instead of each resistor, and a variable DC power supply of 1 (lft) is used instead of each DC power supply, and an operational amplifier (
It is also possible to continuously vary the gain and offset of 21).

Thus, as shown in FIG. 4, the reception frequency f of the high frequency reception signal supplied to the high frequency amplifier circuit RA.

-Δf, the passband center frequency (tuning frequency) of the tuning circuits (2) and (4) becomes this frequency f.

−Δf. For this reason, Figure 5A
As shown in Fig. 2, the amplitude characteristic for the high frequency reception frequency is f when the maximum frequency deviation is ±Δf.

It becomes substantially flat in the range between −Δf and ro+Δf.

Further, as shown in FIG. 5B, the phase characteristics of the high frequency received signal also become approximately flat in the range between fo - Δf and fo + Δf, thereby significantly reducing the distortion of the high frequency received signal in the high frequency amplifier circuit RA.

In addition, since the offset voltage of the operational amplifier (21) is changed according to the value of the tuning control voltage from the PLL (11) as described above, the high frequency amplifier circuit RAO high frequency tuning circuit (
2) and (4) allow reliable tracking.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, the detection output from the detection circuit (9) generates a high frequency signal in the same circuit (2).

This is a case where changing the passband center frequency (tuning frequency) in (4) is omitted and, accordingly, the operational amplifier (21) in the second tuning control voltage generation circuit (25) is omitted. . That is, in FIG. 6, switches 81 to
One end of each series circuit of S4 and DC power supplies E1 to E4 is grounded, and the other end is connected to an operational amplifier (16) through a resistor (23).
) to the inverting input terminal. The other configurations are the same as in FIG. 1.

Note that the present invention is also applicable to electronically tuned AM (radio) receivers.

〔Effect of the invention〕

According to the present invention described above, the frequency characteristics of the tuning control voltage supplied to the local oscillator are corrected so that the tuning frequency of the high frequency tuning circuit approximately follows the tuning frequency, and this corrected tuning control voltage is applied to the high frequency tuning circuit. Since the tracking error of the high frequency amplifier circuit can be significantly reduced.

Therefore, in the case of an electronically tuned FM receiver, the distortion in the high frequency amplification circuit of the high frequency received signal is reduced, and the electronically tuned type A
In the case of the M receiver, the reduction in sensitivity of the high frequency received signal in the high frequency amplification circuit is reduced.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of the present invention, Figure 2 is a characteristic curve diagram showing the frequency characteristics of the output voltage of the operational amplifier (21), and Figure 3 is each voltage-controlled variable capacitor of the high frequency tuning circuit. Figure 4 is a characteristic curve diagram showing the frequency characteristics of the tuning control voltage supplied to the element. Figure 4 is a characteristic curve diagram showing the frequency characteristics of the high frequency tuning circuit and the frequency relationship of the high frequency received signal. Figure 5 is the amplitude frequency in the high frequency tuning circuit. A characteristic curve diagram showing characteristics and phase frequency characteristics, FIG. 6 is a circuit diagram showing a part of another embodiment of the present invention, and FIG. 7 is a circuit diagram of a conventional example. RA is a high frequency amplifier circuit, (2), (4) are a high frequency tuning circuit, (3) is a high frequency amplifier, (5) is a frequency conversion circuit, (6) is a frequency mixer, (7) is a local oscillator, (8)
) is an intermediate frequency amplifier circuit, (9) is a frequency detection circuit, (1
1) is a PLL as a first tuning control voltage generation circuit, (
25) is a second tuning control voltage generation circuit. Figure 2 Figure 3 Chair a Tooth a Mouth Figure 4 General 1 song # Eyes Figure 5

Claims (1)

[Scope of Claims] An electronic device having a high frequency amplification circuit including a tuning circuit, a frequency conversion circuit, an intermediate frequency amplification circuit, a detection circuit, and a first tuning control voltage generation circuit that controls the oscillation frequency of a local oscillator of the frequency conversion circuit. In the tuned receiver, the frequency characteristics of the tuning control voltage from the first tuning control voltage generation circuit are corrected so that the tuning frequency of the tuning circuit approximately follows the tuning frequency, and the corrected tuning control is performed. An electronically tuned receiver comprising a second tuning control voltage generating circuit that supplies voltage to the tuning circuit.